1. Field of the Invention
The present invention relates to an apparatus and method for loading pellets into fuel rods of the type adapted for use in nuclear reactors, and more particularly to an apparatus and method which also identifies undersized pellets and precludes the loading of such undersized pellets into the fuel rods.
2. Description of the Prior Art
Commercial nuclear reactors of the type designed for the generation of electrical power utilize several fuel assemblies, each composed of a large number of fuel rods. Each of the rods in turn contains about 240 fuel pellets, which serve to generate heat during reactor operation.
According to prior practices, the pellets were manually inserted into the fuel rods, by utilizing various stands and tables which support the rods in a fixed position relative to a tray containing a number of columns of fuel pellets. Each column was accurately aligned longitudinally with the open end of its associated fuel rod, and the operator then manually pushed a number of columns of pellets into the rods. The tray was then replaced with a new supply of pellets, and the process repeated until each rod was full. More recently, the pellets have been loaded utilizing vibratory feed tables, note for example the prior patent to Dazen et al, U.S. Pat. No. 3,940,908, and the patent to Tedesco, U.S. Pat. No. 3,965,648.
It is also recognized in the art that the fuel pellets utilized in the fuel rods of a nuclear power generator must be maintained within close size tolerances, since an improperly sized pellet will heat to a nonuniform temperature. While pellet manufacturers employ numerous checks during the manufacturing process to detect improperly sized pellets, it is believed to be possible that an improperly sized pellet could escape detection during manufacture. Any such failure would be particularly acute in the case of a pellet of undersized diameter, since an undersized pellet can be loaded into the rod without difficulty, and thus without being detected during the loading operation.
It is accordingly an object of the present invention to provide an apparatus and method for identifying an undersized cylindrical pellet in an advancing column of pellets.
It is a more particular object of the present invention to provide an apparatus and method which is adapted to detect and segregate an undersized fuel pellet in a column of longitudinally advancing pellets being loaded into a fuel rod adapted for use in a nuclear reactor, and wherein an undersized pellet will be detected and segregated prior to its being loaded into the rod, to thereby provide further assurance that an undersize pellet will not be loaded into the rod.